The attack "proves that these militias are merely a tool that Iran's regime uses to implement its expansionist agenda," tweeted Prince Khalid bin Salman, a son of King Salman.

"The terrorist acts, ordered by the regime in Tehran, and carried out by the Houthis, are tightening the noose around the ongoing political efforts."

The Houthis, which have been battling a Saudi-led military coalition in Yemen for four years, said they carried out Tuesday's drone strikes against the East-West pipeline, which caused a fire but Riyadh said did not disrupt output or exports.

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Other Saudi officials fired off similar tweets, ratcheting up pressure on the kingdom's regional arch enemy amid heightened tension between Washington and Tehran over sanctions and U.S. military presence in the Gulf.

"The Houthis are an integral part of the Revolutionary Guard forces of Iran and follow their orders, as proven by them targeting installations in the kingdom," Minister of State for Foreign Affairs Adel al-Jubeir tweeted.

The ambassador to Yemen followed up, writing that the Houthis had "made Yemen a platform for Iranian terrorism against Yemenis and their interests, and a tool to attack Saudi Arabia."

The coalition, which receives arms and intelligence from Western nations, carried out air strikes on Thursday in and around the Houthi-held capital Sanaa. It intervened in 2015 to restore Yemen's internationally-recognised government.

The drone attack happened two days after four vessels, including two Saudi oil tankers, were damaged by sabotage off the coast of the United Arab Emirates. The other ships were a Norwegian-registered oil products tanker and a UAE-flagged bunker barge.

The UAE has not blamed anyone for that incident, which is being investigated and from which Iran has distanced itself. On Wednesday, Minister of State for Foreign Affairs Anwar Gargash said the UAE would show restraint and was committed to de-escalation.

U.S. officials believe Iran encouraged the Houthis or Iraq-based Shi'ite militias to carry out the attack, two U.S. government sources have said. One source said Washington does not have evidence that Iranian personnel played any direct operational role.

The attacks took place against a backdrop of U.S.-Iranian tension following Washington‘s decision this month to try to cut Tehran's oil exports to zero and beef up its military presence in the Gulf in response to what it called Iranian threats.

Saudi Arabia and the UAE back the sanctions against Iran, a fellow OPEC producer but regional foe.

Tehran has called the U.S. military presence "a target" rather than a threat, and said it would not allow its oil exports to be halted.

Iran's foreign minister has said â€œextremist individualsâ€ in the U.S. government were pursuing dangerous policies and Tehran is not seeking confrontation.